i don't know, there are tons of theory sites that show the muscles in the skull getting tight, something with the galea. there was some study where they put botox into some guys head to relax the muscles and the guy managed to regrow his hair. someone else did it, but it didn't work, but not really sure how it went or if they even did it right.
all those guys that look into it though they think if they do scalp massage or something, it will fix the problem. i don't think it is accurate, i don't think that fixes the problem. its the cortisol is high, or lack of magnesium, or a backed up digestive system, or lack of pregnenlone, i'm not sure what it is exactly, but it causes the muscles in the head to get strained, like on the side of the head. you notice people who are bald, their skull is shiny, like it was stretched out somehow. i don't know the process though.
but it seems like the right course of events, like fungus buildup, lack of vitamin A, digestion problems, it leads to this chain of events where the muscles get strained. it doesn't make sense why it doesn't happen to women though, i don't know why, maybe it's the DHT that causes the muscles to strain, i really don't know as i keep saying lol, but i have felt the muscle strain and felt it relax as well.
I think that the hardening of the scalp is caused by fibrosis. Stiff muscles doesn't explain the pattern, but the location of blood vessels in the head can explain it.